Several problems need to be studied in grey system theory

The problems which remain for further studying in grey system theory are identified. Including the synthesis axiom of degree of greyness for “multiplication” and “division”, how to construct and select a suitable buffer operator? how to select and test a grey prediction model? how to build a negative grey incidence analysis models? the test rules and criteria of grey clustering evaluation models, and on consensus and unified definition of grey combined models, etc.